sPHENIX tracking discussion

[Anthony Frawley <afrawley AT fsu.edu>]

Hi All,

This is a heads-up for trackers.

Chris has just merged coresoftware PR#1555 and macros PR#529. These modify the TPC clustering to use (and store in the cluster) arrival time instead of z as the local coordinate.  That is how the real data will be handled. The details of converting time to global z value are all handled internally by the ActsGeometry class. That change required that the TpcDefs class be moved from packages/tpc to packages/trackbase, since ActsGeometry needs to get the side from the cluster key. You will need to update your coresoftware and rebuild, or your tracking code will break. Also update your macros area to get changes to G4_TPC.C, G4_Tracking.C, and G4_Input.C.

Conversion of TPC cluster time to z position needs the drift velocity. I decided to make ActGeometry the keeper of the (reconstruction, see below) drift velocity, and have any module that needs it request it from ActsGeometry. This is to avoid having the drift velocity be defined in multiple places. The only exception is the utility class tpc/TpcClusterZCrossingCorrection, where I have not yet figured out how to get the (static) drift velocity from ActsGeometry, so it is set from the macro.

When we have data, the drift velocity used in reconstruction will be determined from the data and will not be the same as the one we use in simulations. Following PR#529, the TPC macro defines different drift velocities for the simulations and reconstruction modules. Currently they are set at 8 cm/ns for both, but they can be specified independently in the macro.

 Cheers

Tony